Context.java 文件改为：

public class Context {
   private Strategy strategy;
 
   public Context(){
      
   }

   public SetStrategy(Strategy strategy){
      this.strategy = strategy;
   }

   public int executeStrategy(int num1, int num2){
      return strategy.doOperation(num1, num2);
   }
}

调用改为：

public static void main(String[] args) {
      Context context = new Context();    
      context.SetStrategy(new OperationAdd());    
      System.out.println("10 + 5 = " + context.executeStrategy(10, 5));
      context.SetStrategy(new OperationSubtract());    
      System.out.println("10 - 5 = " + context.executeStrategy(10, 5));
      context.SetStrategy(new OperationMultiply());          System.out.println("10 * 5 = " + context.executeStrategy(10, 5));
}

这样就不用重复的 new Context 了。

// 策略
interface Strategy{
    public function doOperation(int $num1,int $num2):int ;
}

// 加法
class OperationAdd implements Strategy{

    public function doOperation(int $num1, int $num2): int
    {
        // TODO: Implement doOperation() method.
        return $num1 + $num2;
    }
}

// 减法
class OperationSubtract implements Strategy{

    public function doOperation(int $num1, int $num2): int
    {
        // TODO: Implement doOperation() method.
        return $num1-$num2;
    }
}

// 乘法
class OperationMultiply implements Strategy{

    public function doOperation(int $num1, int $num2): int
    {
        // TODO: Implement doOperation() method.
        return $num1 * $num2;
    }
}

class Context{
    private $_strategy;
    public function set_strategy($_strategy)
    {
        $this->_strategy = $_strategy;
    }


    public function executeStrategy(int $num1,int $num2){
        return $this->_strategy->doOperation($num1,$num2);
    }
}
class Demo{
    public static function main(){
        $context = new Context();
        $context->set_strategy(new OperationAdd());
        echo "10 + 5 = ".$context->executeStrategy(10,5).PHP_EOL;
        $context->set_strategy(new OperationSubtract());
        echo "10 - 5 = ".$context->executeStrategy(10,5).PHP_EOL;
        $context->set_strategy(new OperationMultiply());
        echo "10 * 5 = ".$context->executeStrategy(10,5).PHP_EOL;
    }
}

Demo::main();